DNA replication is a crucial step in the cell cycle where cellular DNA must be faithfully copied only once. Failure to do so will result in either incomplete replication or multiple rounds of replication, both of which result in aberrant chromosome numbers. This proposal aims to understand how a protein known as Cdt1, which has been shown in all organisms to be the key player in controlling DNA replication, is regulated. Mis-regulation of Cdt1 levels plays a key role in tumorigenesis, underscoring the importance of this pathway in cancer biology.